Various proposals have heretofore been made for grain type leather-like sheets, and various materials have been produced for them. Many of these have a patterned indented surface of embossed pattern, therefore lacking difference of a glossy feel and a color tone. Specifically, their appearance is monotonous with no three-dimensional and solid feel, and they are unsatisfactory as a material for producing commercial products with high-grade appearance. Recently, improving these have been repeatedly tried, and various proposals have been made for them.
One proposal is to make the valleys of an embossed pattern matted to produce a gloss difference between the valleys and the hills of the embossed pattern, and it is to make the hills glossier to produce a three-dimensional appearance, as in JP-B 59-34821 and 59-33715. Another proposal is to change the color tone between the valleys and the hills of an embossed pattern to thereby make the pattern have a color difference between them and a three-dimensional appearance, as in JP-A 63-42980. Still another proposal is to produce suede-like leather that has a three-dimensional appearance and a color difference by applying a solution or dispersion of an elastic polymer onto the napped face of suede-like leather in the creped pattern shape, as in JP-B 5-45717 and 3-42358. Also proposed is a napped and grainy fibrous sheet produced by forming an embossed pattern on the surface coating layer of a fibrous sheet followed by removing the coating layer on the hills of the pattern by buffing it to thereby raise a fibrous nap on the thus-processed sheet, as in JP-A 63-50580. These produce some interesting appearances, but the embossed pattern formed by these could not substantially have leather-like roughness of valleys and hills and therefore could not express a satisfactory three-dimensional appearance and, in addition, its abrasion resistance is not good.
For improving the surface abrasion resistance and the fluff-dropping resistance of napped fibrous materials, proposed is a method of melting a part of the polymer around the nap roots with a solvent for the polymer to thereby fix the nap roots on the surface, as in JP-A 57-154468. This is effective in some degree for improving the fluff-dropping resistance and the pilling resistance of napped fibrous materials for clothes, but is still impracticable for automobile sheets and interiors that often receive strong abrasion.
On the other hand, JP-A 5-78986 discloses nubuck-type artificial leather of good abrasion resistance, which is produced by infiltrating a polymer elastomer into a melt-blown nonwoven fabric of intermingled ultrafine fibers having a mean fiber diameter of from 0.1 to 6 μm in such a manner that the amount of the polymer elastomer infiltrated into the surface layer side of the fabric is larger than that into the back layer side thereof so as to reinforce the holding power of the ultrafine fibers therein. In this case, however, the ultrafine fibers are firmly bonded to the polymer elastomer and the artificial leather produced could hardly have a soft hand like a natural leather-like.
JP-B 56-16235 discloses an improved method of controlling the bonding of ultrafine fibers to a polymer elastomer of a fibrous material to reduce the dropping of ultrafine fibers with ensuring the soft hand of the fibrous material, which comprises infiltrating a polymer elastomer into a nonwoven fabric of conjugated fibers of two types of polymer substances that differ in the solubility in solvent, before or after one component of the conjugated fibers is extracted away with a solvent to give ultrafine fibers.
JP-A 3-137281 discloses napped artificial leather produced by infiltrating a solution of polyurethane in dimethylformamide (hereinafter this may be abbreviated to DMF) into a nonwoven fabric sheet that is produced by intermingling and integrating a sheet of ultrafine staple fibers having a single fiber fineness of at most 0.5 deniers with a woven or knitted fabric followed by wet-solidifying it, or by infiltrating an aqueous polyurethane emulsion thereinto followed by dry-solidifying, and thereafter fluffing the surface of the thus-processed fibrous sheet with sand paper. In this case, the dry-solidification ensures firm bonding between the ultrafine fibers and the polymer elastomer and is therefore effective in some degree for preventing the dropping of the ultrafine fibers. However, this is defective in that the hand of the artificial leather produced is hard. Another problem with it is that, if the amount of the polymer elastomer to be applied to the fibrous sheet is reduced so as to make the processed sheet have a soft hand, then the surface abrasion resistance of the artificial leather produced lowers.
As mentioned hereinabove, the conventional suede-like artificial leather may have a surface appearance like a natural suede with three-dimensional high-quality expression and a soft hand, but could not have good surface abrasion resistance durable to long-term use for automobile sheets and interiors.
An object of the present invention is to overcome the above-mentioned drawbacks of conventional artificial leather used in the field of automobile sheets and interiors, and to provide artificial leather having good surface abrasion resistance and good appearance and hand like a natural nubuck suitable to use for them.